Inertial actuators are used to actively control vibrations of a structure, e.g., an aircraft fuselage. An inertial actuator is attached to the structure whose vibrations are to be controlled and operated to impart a force on the structure that counteracts the vibrations of the structure. Sensors may be attached to the structure to measure vibrations of the structure. The output of the sensors may be used to control the inertial actuator to generate the force required to counteract the vibrations of the structure. Inertial actuators are based on the principle that accelerating a suspended mass results in a reaction force on the supporting structure. An inertial actuator includes a mass that is connected to a rigid supporting structure by means of a compliant spring. Force is applied to the mass to accelerate the mass and thereby produce the reaction force on the supporting structure. The inertial actuator behaves as a force generator for frequencies above its suspension frequency. Typical inertial actuators are electromagnetic, electrodynamic, or piezoelectric actuators. The present invention relates to electromagnetic inertial actuators.
U.S. Pat. No. 7,288,861 (the '861 patent) discloses an electromagnetic inertial actuator for active vibration control that uses a cylindrical voice coil motor. In the '861 patent, a moving armature is suspended above a base by an array of flexure stacks. The array of flexure stacks is coupled at its center to the moving armature and at its ends to the top ends of vertical support flexures. The lower ends of the vertical support flexures are fastened to the base. The moving armature includes a tubular shell sleeve coaxially surrounding a cylindrical core, which is made of two permanent magnets and corresponding pole plates. A soft iron shell yoke plate attached to one of the magnets and the top end of the tubular shell sleeve magnetically and mechanically links the cylindrical core to the tubular shell sleeve. The two permanent magnets provide two magnetically-charged annular gaps between the pole plates and the inner wall of the tubular shell sleeve. Two voice coils, mounted on the base, are centered in the annular gaps. When the coils are energized, the windings in the coils interact with the magnetic flux in the annular gaps to vibrate the moving armature in a vertical direction as enabled by flexing of the flexure stacks and vertical support flexures.
U.S. Pat. No. 7,550,880 (the '880 patent) discloses a folded flexure system for cylindrical voice coil motors. The folded flexure system may be implemented in one or more tiers, with each tier of the folded flexure system comprising two or more triad array members. Quad array members are also disclosed. Each triad array member includes three compliant span elements—the two outer span elements are half-width while the central span element is full width. In one disclosed embodiment, the outer span elements are attached to the armature shell of a voice coil motor at one end and to a yoke/idler fastening at another end. The central span element is attached to a pedestal of the base at one end and to a yoke/idler fastening at another end. A permanent magnet within the armature shell sets up a magnetically charged annular gap between its circular pole piece and the inner wall of the armature shell. A coil/bobbin assembly attached to the base supports a coil in the annular magnetically charged gap. As in the '861 patent, when the coil is energized, the windings in the coil interact with the magnetic flux in the air gap to exert force that drives the armature mass along a vertical stroke axis. The vertical motion of the armature mass is enabled by symmetrical flexing of the folded flexure system.